The present invention relates to a laser module, and more particular to an uncooled semiconductor laser module adapted for use in a fiber optics communication network.
Laser module designs are useful for analog transmission, e.g., CATV, personal communication systems (PCS), cellular, and for low bit rate digital transmission at a bit rate of about one gigabit/second or below, and for high bit rate digital transmission, e.g., transmission at a bit rate greater than about one gigabit/second.
Some of the laser module designs are cooled. Such designs often utilize a thermal electric cooler (TEC) to provide cooling, or heating, depending upon the voltage polarity used, to the laser module. The presence of the TEC presents several disadvantages. One disadvantage is that the TEC increases the size of the laser module, making the module bulky. Another disadvantage is that the TEC adds to the cost of the laser module. Yet another disadvantage is that the presence of the TEC creates the need for a greater number of electrical connections which must be performed, adding further to the cost of the module. An example of such a laser module design is a cooled ILM (Isolated Laser Module) which is capable of use in analog CATV, analog personal communication systems (PCS), analog cellular and up to 2.5 gigabit/second digital transmissions.
Some laser module designs incorporate what is termed a butterfly configuration. The butterfly configuration is a configuration by which the laser module is electrically connected to a circuit board. In a butterfly configured design, the electrical leads are directly connected with the optical subassembly portion of the laser module. With such a design, the loss of bit speed due to signal degradation due to multiple reflections is lessened, and a transmission rate in excess of ten gigabits/second is achievable. A disadvantage to such a design is that it is prohibitively expensive to manufacture and/or test butterfly configured laser modules in high volume.
The disadvantages of the conventional laser module designs are overcome to a great extent by the present invention, which relates to an uncooled laser module adapted to receive and input radio frequency signals to a laser at direct current (DC) to ten gigahertz. This is accomplished through the inclusion of two pin configurations in a single laser module package. In a preferred embodiment of the laser module, there is included signal-ground circuitry matching an industry-wide standard capable of receiving and transmitting radio frequency (RF) signals to a laser at a bandwidth below about one gigahertz and ground-signal-ground circuitry for a high performance configuration capable of receiving and transmitting RF signals to a laser at a bandwidth up to ten gigahertz.
In an aspect of the present invention, the ground-signal-ground circuitry includes a signal pin, two ground pins, and a first characteristic line, such as a coplanar waveguide, in electrical connection with the ground and signal pins and with a metal pad, a second characteristic line, such as a microstrip, and a microstrip ground. The metal pad and microstrip ground act as grounds for an RF signal input from a driver to the signal pin, and transmitted therefrom through the coplanar waveguide and the microstrip and on to an optical subassembly including a laser. Further, the microstrip has a specific impedance and a specific electrical length.
In another aspect of the present invention, the signal-ground circuitry includes a signal pin, a ground pin, and a first characteristic line, such as a coplanar waveguide, in electrical connection with the signal pin, the ground pin, and two metal pads. One of the metal pads acts as a ground for an RF signal input from a driver to the signal pin, and transmitted therefrom through the coplanar waveguide and the other metal pad and on to an optical subassembly including a laser.
In another aspect of the present invention, the ground pin of the signal-ground circuitry is the signal pin of the ground-signal-ground circuitry.
The foregoing and other advantages and features of the invention will be more readily understood from the following detailed description of the invention, which is provided in connection with the accompanying drawings.